376 



THE VOYAGE OF H.M.S. CHALLENGER. 



B. Marginal plates equal to or smaller than the other plates. 



a. Papulae distributed throughout the abactinal area. Abactinal plates 



thick, crescentiform, devoid of internal processes . . . Asterinin^;. 

 a. Abactinal plates not imbricated ; covered with spines . . . Patiria. 

 h. Abactinal plates imbricated throughout the abactinal area, or 

 only in definite regions. 



a. Rays cylindrical, more or less elongate. Disk small. 

 "With a definitely and sharply defined band of 

 crescentiform plates along the median area of 



the rays Ncpanthia. 



/3. Rays and body flat. Disk large. 



i. Abactinal plates more or less imbricated through- 

 out, and bearing spinelets at the free edge, or 

 covered with granules. All the abactinal 



plates subsimilar . Asterina. 



ii. Abactinal plates imbricating only near the 

 margin, the others spaced apart ; covered with 

 naked skin Disasterina. 



b. Papulae confined to the radial regions. Abactinal plates in the median 



regions stellate. Abactinal plates thin, scale-like, with elongate 



internal prolongations Palmipedin^;. 



a. Abactinal plates bearing tufts of spinelets. No membrane or 



granules. Papulae in a single row on each side of the 



median radial line Palmipcs. 



b. Abactinal plates covered with membrane, hearing granules. 



No tufts of spines. Papulae in several rows on each side 



of the median interradial line ...... Stegnaster. 



Subfamily Ganeriin,e, Sladen, 1888. 

 Genus Cycethra, Bell. 



Cycethra, Bell, Proc. Zool. Soc. Lond. 1881, p. 96. 



This genus was established by Professor Jeffrey Bell for the reception of a starfish dis- 

 covered by Dr Coppinger in Trinidad Channel during the surveying voyage of H.M.S. 

 "Alert" in the Strait of Magellan and on the coast of Patagonia. The remarkable com- 

 bination of characters presented by that form was noticed by Bell, and duly referred to 

 in his description ; and the new species appear to fully bear out the " mixed " character of 

 Cycethra as regards its morphological relationships. The genus would seem to have a 

 limited distribution, but appears to possess a considerable amount of specific plasticity 

 within that area. Its alliance to the very local genus Ganeria is striking, and when the 

 two forms are studied together, I think there will remain little doubt that Cycethra 

 and Ganeria are near neighbours in the zoological scale as well as in geographical 

 position. 



